Eric Anholt at Intel has a new Mesa GLSL patch to add a new pass for their compiler that decreases the number of instructions and can result in performance improvements.
The new GLSL pass in their compiler is CSE, constant sub-expression elimination. The CSE pass ran at the GLSL IR level is still rather simple but it's leading to a reduction in the number of generated command instructions for shaders. Eric noted that for the Unigine Tropics test the frame-rate went up by 11% with this new pass due to its heavy GL Shading Language usage. However, no metrics were provided for other GLSL-using Linux games.
The nearly 600 line patch for Mesa can be found right now on the Mesa development list
. Once this new shader compiler pass is in the Mesa Git tree it will be benchmarked at Phoronix.